Method of manufacturing bundles of very thin magnetic wires



M. P. PRACHE METHOD OF MANUFACTURING BUNDLES Sept. 20, 1955 2,718,049

0F VERY THIN MAGNETIC WIRES Filed Jan. 1949 INVENTOR.

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United States Patent METHOD OF MANUFACTURING BUNDLES OF VERY THINMAGNETIC WIRES Marie Pierre Prache, Versailles, France, assignor toSociete Lignes Telegraphiques & Telephoniques, a corporation of FranceApplication January 6, 1949, Serial No. 69,558

Claims priority, application France January 16, 1948 3 Claims. (Cl.29155.61)

This invention relates to processes for manufacturing bundles of verythin wires formed of a magnetic metal particularly for use in highfrequency alternating current equipment.

Very thin metallic wires have hitherto been manufactured by reducing thediameter of a given wire (herein referred to as a primary wire) bysuccessive passes through dies of diminishing diameter. With very thinwires this reduction of diameter presents many practical difficultiesand the output per hour of a wire drawing machine (which output isapproximately proportional to the cross section of the wire being drawn)falls off rapidly when small diameter wires are being drawn therebyresulting in a high cost price of such wires. Consequently, wires havinga diameter below 50 thousandths of a millimetre are now used only whentheir use is unavoidable and when the required quantity of Wire issmall, such as, for example, in the manufacturing of the moving coils ofelectrical measuring instruments.

One of the domains in which it would be most desirable to take advantageof processes for manufacturing very thin metallic wires at low cost isthat of magnetic materials for use in components of high frequencyalternating current equipment. These materials must be divided to cutdown the prejudicial action of eddy currents which give rise, on the onehand, to a loss of energy which diminishes the quality factor of thewindings and, on the other hand, to an antagonistic magnetic field whichis opposed to the principal field and reduces the inductive effect ofthe material. It can be shown that this prejudicial action isproportional to the second power of the frequency of operation of theequipment and to the second power of the thickness of the strips, or ofthe diameter of the wires of which a component may be made. It followstherefore that the finer are the constituent wires of the component, thehigher is the frequency at which the component can be used. Thus, in themanufacture of high quality inductance cores for use at 100 kilocyclesper second it is necessary to use wires having a diameter of aboutthousandths of a millimetre, and in the manufacture of such cores foruse at 250 kilocycles per second, it is necessary to use wires of about6 thousandths of a millimetre diameter.

According to the present invention there is provided a process formanufacturing bundles of very thin magnetic metal wires which consistsin drawing primary metallic wires enclosed within a metallic sheath, thesaid metallic wires being kept separated, (a) from one another and (b)from the sheath by a friable material or a powder composed of very smallparticles.

The powder particles, which may be those of a layer of oxide or ofanother compound deposited upon the surface of the wires to be drawnserves, as stated, to separate the wires, and at the same time toprevent the wires from adhering to one another or to the sheath and,further, to insulate the wires electrically.

It is evident that as the sheath has an external diameter considerablygreater than that of the wire or wires being 2,718,049 Patented Sept.20, 1955 H drawn, the usual practical difiiculties met with in thedrawing of very thin wires are avoided. Furthermore, a great number ofwires enclosed within the same sheath may of course be drawnsimultaneously, thereby greatly reducing the cost price of the Wires.

The invention will now be described with reference to certain specificembodiments given solely by way of illustrative examples. In thedrawings:

Fig. l is a diagrammatic sectional view of a first embodiment;

Figs. 2 and 3 are similar views of variations from the form of Fig. l;and

Fig. 4 is a view to a larger scale of a composite form suitable forrepeated treatment.

The following description of one manner in which the process accordingto the invention may be carried out, is more particularly directed tothe manufacture of a material suitable for magnietic cores and windings.

The invention is based on the experimental fact that when a bundle ofmetallic wires which are either bare or separated from one another by afriable or pulverulent material are subjected to a drawing process whenenclosed within a common cylindrical sheath, the sheath and itsenclosures are drawn as a whole, as if it were a homogeneous material.

It is advisable to insert a separating material between the wires with aview to avoiding the sticking together of the wires. wires have to bedrawn together and if they are intended to preserve a circularcrosssection they must be surrounded by a sufficient quantity ofseparating material to prevent them from being flattened one against theother.

In magnetic cores used for alternating currents, it is necessary, forthe purposes of limiting the losses due to eddy currents to ensure that,in the final product, the individual wires should be electricallyinsulated from each other. In order to make it possible to obtain, bythe above-described process, a bundle of wires electrically insulatedindividually from each other, it just suffices to use an electricallyinsulating material as separating material.

The separating material used in the process must be capable ofwithstanding, without losing its separating or insulating properties,the effects of the annealing temperature of the metals of the wires andthe sheath. For example, use may be made, as separating material, ofmetallic oxides such as magnesia, alumina, copper-oxide, zinc-oxide, andiron-oxide; or else mixtures of oxides and metallic salts which arestable at high temperatures, such as, silicates, may be used.

The separating material used may be put in position for the process inany known manner. It may for instance be used in the form of an emulsionof adequate consistency, prepared by dissolving or suspending theseparating material in a liquid, the wires being then immersed in theemulsion and dried.

In Fig. l, the wires 1, coated with the separating material 2, areassembled into a bundle and then inserted into the sheath 3, which canfor instance be constituted by a metallic tube. During the assembling ofthe bundle and its insertion into the sheath, a certain amount ofpowdered separating material can be added in order to insure adequatefilling of the sheath.

As shown in Fig. 2, the insertion of the bundle into the sheath will bemuch easier if a longitudinally slit tube 4 is used as the sheath, sucha tube being easily formed by the longitudinal folding of a metallicstrip to surround the bundle of primary wires 1. A tube with twolongitudinal slits can be also formed by folding two strips round thebundle, each of which covers half of the bundle periphery. It has beenexperimentally as- It must be noted, moreover, that if several certainedthat the longitudinal slits do not hinder the drawing process.

In order to prevent the wires or the separating material from coming outof the sheath by way of the slit or slits therein, as shown in Fig. 3the slit sheath 4 may be surrounded by a second slit sheath 5, the slitor slits of the second sheath being disposed in such a manner that theydo not coincide with those of the first sheath.

The sheath enclosing the wires is then drawn, with reheating betweensuccessive passes according to the known process. If it is required toproduce very thin wires it may be advantageous to avoid the use of verysmall drawing diameters and to stop the drawing process at a given stagethereof, to remove the sheath by one of the processes hereinafter to bedescribed and to make up a fresh sheath of greater diameter inaccordance with Fig. 4 to enclose several bundles 6 of the drawn wires,whereupon the drawing process is repeated using as primary wire, wirewhich has been already drawn. This use of the drawn wire bundles may berepeated as often 1.!

as necessary.

To remove the metallic sheath or sheaths, recourse may be had tochemical, mechanical or thermal processes.

If a chemical process is chosen, the sheath is dissolved away by anappropriate reagent, but this method has the drawback of exposing theseparating material and the wires to the action of the reagent used,unless the reaction is stopped when the action of the reagent upon thesheath is just at its end. If this is not possible,

it is advisable to use different metals for the sheath and 2- the wiresand to choose a reagent which does not attack the wires. The wires may,for example, be made of a magnetic nickel-iron alloy and be drawn iniron sheaths, the iron being afterwards dissolved in sulphuric acidwhich does not attack the nickel-iron alloy. However, I

if the wires are intended for use in a magnetic core or winding, it isgenerally necessary to reinsulate them, for example, by varnishing orenamelling.

If a mechanical process is chosen, the removal of the sheath may beeffected by a device similar to that used for stripping the cover fromlead-sheathed electric cables, i. e., by cutting the sheath at both endsof a diameter and then taking off the two strips so obtained by pushingthem aside. This process will of course be easier to apply if slitsheaths, as described above, are

used.

If a thermal process is chosen, a metal with a meltingpoint inferior tothat of the wires and the separating material is used to compose thesheath or sheaths which are then removed by melting, the coated bundlebeing drawing can be used directly for certain applications and,

in particular, for making magnetic cores or windings. The mechanicalresistance of the bundle of wires may, if necessary, be increased byslight twisting. If the bundle is intended to have a shape other thancircular, for example, a strip-like shape, then the drawing process isfinished by one or several rollings. Resistance to friction andsuperficial insulation of the bundle may also be increased by any of theknown processes such as, for example, varnishing or enamelling.

If the bundles are used to compose induction coils or transformer cores,the mechanical resistance of the cores may be increased by compressingthem in moulds and/ or L by impregnating them with an insulating varnishas are the loading coils of telephone cables.

What is claimed is:

1. A process for manufacturing bundles of very thin magnetic wires toprovide a flexible magnetic material for use in high frequencyelectrical equipment; said process comprising the steps of immersingprimary ferromagnetic material wires in an emulsion of a metalliccompound having electrical insulating properties, said metallic compoundbeing selected from the group consisting of metallic oxides, metallicsilicates and mixtures of the same, and being in suspension within saidemulsion, drying the primary wires after immersion to leave a coveringlayer thereon of the electrical insulating metallic compound, assemblingtogether a bundle of the covered wires and enclosing the bundle within ametal casing so that the wires are insulated from each other and fromsaid casing by the electrical insulating metallic compound, drawing thecasing with the bundle of covered wires therein until the wires are eachreduced to a diameter of less than 0.03 mm., annealing the drawn casingand wires, and removing the casing from the bundle of wires withoutdisturbing the covering of electrical insulating metallic compound oneach of the wires so that the bundle of very fine wires electricallyinsulated from each other provides a flexible magnetic material.

2. A process for manufacturing bundles of very thin magnetic wires toprovide a flexible magnetic material for use in high frequencyelectrical equipment; said process comprising the steps of immersingprimary ferromagnetic material wires in an emulsion of a metallic oxidein suspension having electrical insulating properties, drying theprimary wires after immersion to leave a covering layer thereon of theelectrical insulating metallic oxide, assembling together a bundle ofthe covered wires and enclosing the bundle within a metal casing so thatthe wires are insulated from each other and from said casing by theelectrical insulating metallic oxide, drawing the casing with the bundleof covered wires therein until the wires are each reduced to a diameterof less than 0.03 mm., annealing the drawn casing and wires, andremoving the casing from the bundle of wires without disturbing thecovering of electrical insulating metallic oxide on each of the wires sothat the bundle of very fine Wires electrically insulated from eachother provides a flexible magnetic material.

3. A process according to claim 2; wherein said metallic oxide ismagnesium oxide.

References (liter! in the file of this patent UNITED STATES PATENTS Re.20,507 Andrews et al. Sept. 14, 1937 874,908 Fritts Dec. 24, 19071,274,952 Speed Aug. 6, 1918 1,292,659 Speed Jan. 28, 1919 1,525,840Weed Feb. 10, 1925 1,650,972 Backer Nov. 29, 1927 1,850,181 Roseby Mar.22, 1932 1,981,468 Roseby Nov. 20, 1934 1,991,143 Ehlers Nov. 20, 19342,050,298 Everett Aug. 11, 1936 2,064,184 Stevens Dec. 15, 19362,077,682 Everett Apr. 20, 1937 2,088,446 Specht July 27, 1937 2,215,477Pipkin Sept. 24, 1940 2,338,045 Leonard Dec. 28, 1943 2,341,235 PalmerFeb. 8, 1944 2,383,118 Ferenci Aug. 21, 1945 2,493,609 Young Jan. 3,1950 2,513,161 Friend June 27, 1950

1. A PROCESS FOR MANUFACTURING BUNDLES OF VERY THIN MAGNETIC WIRES TOPROVIDE A FLEXIBLE MAGNETIC MATERIAL FOR USE IN HIGH FREQUENCYELECTRICAL EQUIPMENT; SAID PROCESS COMPRISING THE STEPS OF IMMERSINGPRIMARY FERROMAGNETIC MATERIAL WIRES IN AN EMULSION OF A METALLICCOMPOUND HAVING ELECTRICAL INSULATING PROPERTIES, SAID METALLIC COMPOUNDBEING SELECTED FROM THE GROUP CONSISTING OF METALLIC OXIDES, METALLICSILICATES AND MIXTURES OF THE SAME, AND BEING IN SUSPENSION WITHIN SAIDEMULSION, DRYING THE PRIMARY WIRES AFTER IMMERSION TO LEAVE A COVERINGLAYER THEREON OF THE ELECTRICAL INSULATING METALLIC COMPOUND, ASSEMBLINGTOGETHER A BUNDLE OF THE COVERED WIRES AND ENCLOSING THE BUNDLE WITHIN AMETAL CASING SO THAT THE WIRES ARE INSULATED FROM EACH OTHER AND FROMSAID CASING BY THE ELECTRICAL INSULATING METALLIC COMPOUND, DRAWING THECASING WITH THE BUNDLE OF COVERED WIRES THEREIN UNTIL THE WIRES ARE EACHREDUCED TO A DIAMETER OF LESS THAN 0.03 MM., ANNEALING THE DRAWN CASINGAND WIRES, AND REMOVING THE CASING FROM THE BUNDLE OF WIRES WITHOUTDISTURBING THE COVERING OF ELECTRICAL INSULATING METALLIC COMPOUND ONEACH OF THE WIRES SO THAT THE BUNDLE OF VERY FINE WIRES ELECTRICALLYINSULATED FROM EACH OTHER PROVIDES A FLEXIBLE MAGNETIC MATERIAL.